Synthesis Of Aligned Carbon Nanotubes Research Articles

Controllable synthesis of N-doped aligned carbon nanotubes from melamine-based carbon by water-assisted chemical vapor deposition

N-doped well-aligned thin multiwall carbon nanotubes (CNTs) have been prepared by a facile water-assisted chemical vapor deposition (CVD) process using melamine as both the carbon precursor and N-dopant and ferrocene as both the catalyst and carbon precursor. It is shown that the synthetic temperature has strong effects on the growth of carbonaceous structure. Carbon films started to grow at reaction temperature of 700 °C, and the optimal temperature for the synthesis of aligned CNTs, based on the experiment results, was found to be 900 °C. The lengths of the CNTs can be tuned by changing the annealing time of the pyrolysis process, it could reach as long as 40.2 μm. The atomic percentage of nitrogen doping in aligned CNTs could be achieved to 1.71%. It was found that there were many joints and defects in the as-prepared CNTs which may offer more nucleation sites on the chemically inert CNT surface for various specialized applications such as supercapacitor.

Resonance Raman and IR spectroscopy of aligned carbon nanotube arrays with extremely narrow diameters prepared with molecular catalysts on steel substrates.

Carbon nanotubes (CNTs) are considered promising for a large range of emerging technologies ranging from advanced electronics to utilization as nanoreactors. Here we report a controlled facile synthesis of aligned carbon nanotubes with very small dimensions directly grown on steel grid substrates via two-step catalytic chemical vapor deposition (CCVD) of a molecular catalyst (ferrocene) with ethylene as the carbon source. The system is characterized by resonance Raman spectroscopy and the results show single walled carbon nanotube (SWCNT) arrays composed of 0.80 nm to 1.24 nm semiconducting CNTs, as analyzed using Kataura analysis, which is approaching the lowest diameters attainable for SWCNTs. The G+ and G- mode splitting, G- line shapes and ring breathing modes (RBMs) are analyzed to characterize the CNTs. The approach results in close packed and vertically aligned SWCNT bundles formed into hair shapes, with some contribution from multiwall CNTs (MWCNTs). IR spectroscopy is utilized to characterize the edge/defect states that have the ability to form esters and ether bonds in the as-prepared CNTs. The stepwise deposition of the catalyst followed by the carbon source gives control over the formation of small diameter single walled carbon nanotubes (SWCNTs). The utilization of molecular catalysts for narrow diameter growth directly on steel grid substrates forms a promising approach for producing cost-effective CNT substrates for a plethora of sensing and catalytic applications.

An Overview of Selected Catalytic Chemical Vapor Deposition Parameter for Aligned Carbon Nanotube Growth

Aligned carbon nanotube (A-CNT) has been extensively studied due to their high potential in many applications. Despite the fact that catalyst preparation is the key role to grow A-CNTs, the parameter of catalytic chemical vapor deposition (C-CVD) also influences A-CNT growth and its morphologies. This review focused to critically synthesize the published data in scientific report on A-CNT for better understanding the C-CVD parameter governing vertically A-CNT growth. The review will mainly discuss the influence of C-CVD processing temperature, C-CVD processing time, and carbon feedstock in A-CNT growth and its effects on A-CNT morphologies. Challenges and future perspectives in the synthesis of aligned carbon nanotubes have also been discussed.

Complementary metal-oxide-semiconductor-compatible and self-aligned catalyst formation for carbon nanotube synthesis and interconnect fabrication

We have for the first time developed a self-aligned metal catalyst formation process using fully CMOS (complementary metal-oxide-semiconductor) compatible materials and techniques, for the synthesis of aligned carbon nanotubes (CNTs). By employing an electrically conductive cobalt disilicide (CoSi2) layer as the starting material, a reactive ion etch (RIE) treatment and a hydrogen reduction step are used to transform the CoSi2 surface into cobalt (Co) nanoparticles that are active to catalyze aligned CNT growth. Ohmic contacts between the conductive substrate and the CNTs are obtained. The process developed in this study can be applied to form metal nanoparticles in regions that cannot be patterned using conventional catalyst deposition methods, for example at the bottom of deep holes or on vertical surfaces. This catalyst formation method is crucially important for the fabrication of vertical and horizontal interconnect devices based on CNTs.

Synthesis of aligned carbon nanotubes by thermal chemical vapor deposition

Single crystal silicon was found to be very beneficial to the growth of aligned carbon nanotubes by chemical vapor deposition with C2H2 as carbon source. A thin film of Ni served as catalyst was deposited on the Si substrate by the K575X Peltier Cooled High Resolution Sputter Coater before growth. The growth properties of carbon nanotubes were studied as a function of the Ni catalyst layer thickness. The diameter, growth rate and areal density of the carbon nanotubes were controlled by the initial thickness of the catalyst layer. Steric hindrance between nanotubes forces them to grow in well-aligned manner at an initial stage of growth. Transmission electron microscope analysis revealed that nanotubes grew by a tip growth mechanism.

Synthesis of aligned carbon nanotubes by microwave chemical vapour deposition and investigation of their covalent bonding with antibodies for bioapplications

Synthesis of aligned carbon nanotubes arrays and their covalent bonding with antibodies for potential antibody-antigen immunosensing are presented. Aligned carbon nanotubes were prepared by a template assisted microwave chemical vapour deposition. This method will produce less amorphous carbon due to the existing temperature gradient. The effect of catalysts for carbon nanotubes growth was studied. A post treatment process was developed to remove the amorphous carbon layer and partially etch the template so that nanotubes tips were exposed. After functionalisation of carbon nanotubes arrays, fluorescence-labelled IgG antibodies were attached to their surface by a two-step process of diimide-activated amidation. The covalent bonding between antibodies and carbon nanotubes arrays was evaluated by a fluorescent microscope. A stronger bonding was observed from functionalised carbon nanotubes than unfunctionalised ones. It is believed that both the alignment of carbon nanotubes and their covalent bonding with antibodies play important roles for immunosensors with high sensitivity and selectivity.

Template assisted synthesis of aligned carbon nanotubes and their supercapacitor applications

Multi-walled Carbon Nanotubes (MWNT) have been synthesised by the pyrolysis of acetylene over a well-ordered porous Anodic Aluminium Oxide (AAO) template. Structural and morphological characterisations of MWNT have been carried out using powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM and HRTEM) and Raman spectroscopy. Electrochemical characteristics of supercapacitor fabricated from purified MWNT have been investigated. Capacitance measurements have been performed by cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy. Maximum specific capacitance of 86 F/g was obtained for MWNT electrodes prepared with purified MWNT synthesised using AAO template.

Simultaneous catalyst deposition and growth of aligned carbon nanotubes on SiO2∕Si substrates by radio frequency magnetron sputtering

Radio frequency magnetron sputtering has been used for the synthesis of aligned carbon nanotubes (CNTs) on a SiO2∕Si substrate, with simultaneous in situ catalyst deposition. This method allows the use of substrates without the need of a surface predeposition of catalytic particles. In particular, among the metals considered, we observed the formation of CNTs using W or Ni as catalysts. Only in the case of Ni did we find that the CNTs are aligned along the target-substrate direction, unlike the randomly oriented CNTs observed when W was used as catalyst. Scanning and transmission electron microscopies show that the catalytic Ni nanoparticle is found mostly on the tip of the obtained bamboolike CNTs, while W nanoparticles are encapsulated inside hollow nanotubes, at different points along their length. We ascribe not only the observed structural differences to the size of the W and Ni particles but also to a different diffusion behavior of C in the two kinds of metallic clusters.

Ex situ and in situ catalyst deposition for CNT synthesis by RF-magnetron sputtering

Radio frequency magnetron sputtering has been used for the synthesis of aligned carbon nanotubes (CNTs) on SiO 2/Si substrate. The results were obtained by depositing catalytic nano-particles in advance (ex situ) or simultaneously to the C deposition (in situ), which have been compared showing that the oxidation of the metal catalyst deposited in advance is detrimental for the good outcome of the CNTs growth. An in situ catalyst deposition allows to get rid of the contamination problem and to grow aligned CNTs on a substrate, as shown by scanning electron microscopy. Transmission electron microscopy shows that the so-achieved CNTs own a bamboo-like structure and the catalytic Ni nanoparticle is on the tip of the CNTs. Our method allows to perform catalyst deposition and growth of CNT on a SiO 2/Si substrate simultaneously and its use can be extended to a variety of catalytic elements and substrates, in principle without many efforts.

Effects of Temperature and Catalyst Concentration on the Growth of Aligned Carbon Nanotubes

The effects of preheating and pyrolysis temperatures and catalyst concentration on the synthesis of aligned carbon nanotubes (CNTs) using ferrocene as the catalyst and xylene as the carbon source in chemical vapor deposition were experimentally studied. The as-grown aligned CNTs were characterized by field emission scanning electron microscopy, transmission electronic microscopy, high-resolution transmission electronic microscopy, and Raman spectroscopy. The growth rate, the diameters, and the degree of crystal structure of the aligned CNTs were all found to depend on the preheating and pyrolysis temperatures and the catalyst concentration. The optimized conditions for the growth of aligned CNTs resulted in a rapid growth rate of 20.4 μm/min, with the CNTs having a good, uniform crystal structure, and clean surfaces with little amorphous carbon. The results also show that higher preheating temperatures and lower ferrocene concentrations favor the growth of single-walled CNTs.

Synthesis of Aligned Carbon Nanotubes by Inductively Coupled Plasma Chemical Vapor Deposition

Inductively coupled plasma chemical vapor deposition combined with substrate biasing using a gas mixture of methane and hydrogen was applied to low-temperature synthesis of aligned carbon nanotubes and nanofibers. We found that the resultant carbon nanotubes, which were grown at 500°C, were aligned perpendicular to the substrate, and the aligned carbon nanofibers were synthesized even at a growth temperature as low as 200°C. The growth mechanism of the aligned carbon nanotubes and carbon nanofibers is discussed in terms of the moderate etching of carbon deposit by hydrogen species in inductively coupled plasma.

Catalyst influence on the flame synthesis of aligned carbon nanotubes and nanofibers

Since prepared substrates offer an appropriate method for the selective production of uniform arrays of aligned CNTs and CNFs, it is important to illustrate the influence of different catalysts on the resulting nanostructures. This investigation characterizes the activity of three catalysts—iron in alloyed form as stainless steel, nickel, and platinum—on carbon nanostructure formation under identical conditions in an ethylene/air nonpremixed flame. We have synthesized well-aligned multi-walled CNTs (on Ni) and CNFs (on stainless steel). The third transition metal Pt produces CNF structures of a different kind, and its activity has not been previously characterized in flames. The catalyst and gas-phase conditions leading to the formation of these different structures are discussed.

Synthesis of aligned carbon nanotubes by DC plasma-enhanced hot filament CVD

Vertically aligned carbon nanotubes (CNTs) films have been prepared by a direct current plasma-enhanced hot filament chemical vapour deposition method. The growth of multi-walled carbon nanotubes on metal (Fe, Co, Ni) precoated silicon substrate are studied between 500 and 1000 °C using gas mixtures of methane, hydrogen and argon. The influence of substrate pre-treatment, substrate voltage and deposition temperature on the structure and the alignment of the CNTs are discussed. In dependence on thickness of the thin metal layers, thermal pre-treatment or hydrogen plasma etching and plasma parameters during the deposition process different carbon nanostructures, especially regarding tube diameter, morphology and arrangement could be proved. Transmission electron microscopy images of isolated tubes showed an imperfectly trained tubular structure of graphite shells, formed as ‘bamboo’-like shapes with partly crystalline metal droplets on the tip. Because the alignment of the tubes is induced by the discharge voltage and the electrical field, the characteristic plasma parameters as plasma potential, electron energy and electron density, measured by Langmuir probe investigations were discussed.

Synthesis of aligned carbon nanotubes in organic liquids

A simple and novel method was developed for efficient synthesis of aligned multiwalled carbon nanotubes (CNTs) in methanol and ethanol under normal pressure. The CNTs' alignment and structures were investigated using Raman scattering and x-ray diffraction spectroscopy. A unique kind of coupled CNT was synthesized in which one rotated to the left and one rotated to the right. Chains periodically bridged the coupled CNTs. The growth mechanism of the CNTs within organic liquid is proposed to be a catalytic process at the Fe film surface in a dynamic and thermal nonequilibrium condition in organic liquids.

Synthesis of aligned carbon nanotubes

Carbon nanomaterials seem to be most attractive because of their fascinating features. Carbon nanotubes emerged recently as unique nanostructures with remarkable mechanical and electronic properties. Future applications will require a fabrication method capable of producing uniform carbon nanotubes with well-defined and controllable reproducibility of their properties. In this review, recent results addressing rational and efficient methods to obtain aligned arrays of these one-dimensional carbon nanomaterials will be discussed.

Liquid phase synthesis of carbon nanotubes

A novel method has been developed for synthesis of aligned carbon nanotubes (CNTs) by simply electrically heating a substrate in organic liquids. Si substrates with a thin Fe film cover were electrically heated to 500–1000°C in organic liquid. Aligned mutiwalled CNTs were grown and stick well on the Si substrates by using methanol and ethanol. The top ends of the nanotubes were closed with seamless caps. Some other shaped CNTs have also been synthesized, in particular, a special kind of coupled CNT of which the structure of one CNT is left hand rotated and the other right hand rotated with bridging chains between them. The growth mechanism of CNTs in organic liquids is proposed to be related to the adsorption and decomposition of organic radicals at the catalytic substrate surface under in-equilibrium thermal and dynamic conditions.

Large-Scale Synthesis of Aligned Carbon Nanotubes

Large-scale synthesis of aligned carbon nanotubes was achieved by using a method based on chemical vapor deposition catalyzed by iron nanoparticles embedded in mesoporous silica. Scanning electron microscope images show that the nanotubes are approximately perpendicular to the surface of the silica and form an aligned array of isolated tubes with spacings between the tubes of about 100 nanometers. The tubes are up to about 50 micrometers long and well graphitized. The growth direction of the nanotubes may be controlled by the pores from which the nanotubes grow.